In a conventional liquid crystal display device, there is provided a TFT substrate in which pixel electrodes, thin film transistors (TFTs) and the like are arranged in a matrix form and a counter substrate in which color filters and the like are formed at locations corresponding to the pixel electrodes of the TFT substrate is disposed opposite to the TFT substrate. A liquid crystal is interposed between the TFT substrate and the counter substrate. Then, an image is formed by controlling the transmittance of light of the liquid crystal molecules for each pixel.
In such a conventional liquid crystal display device, it is necessary to exactly match the pixel electrodes formed in the TFT substrate to the color filters formed in the counter substrate. However, the positioning accuracy of the TFT substrate and the counter substrate is about 3 to 5 μm, which should be taken into account in the allowance of the pattern. As a result, the transmittance of a liquid display panel is reduced.
On the other hand, when the color filters are formed on the side of the TFT substrate, the TFT substrate and the counter substrate can be roughly positioned to each other. In other words, when the color filters are formed on the side of the TFT substrate, the alignment accuracy of the color filters with respect to the wiring and the TFTs in the TFT substrate can be set in accordance with the mask alignment accuracy in photo processing, and can be set to about 1 μm. JP-A No. 357828/2002 describes a configuration in which color filters are formed on the side of the TFT substrate as described above.
Liquid crystal display devices have been used in a wide range of applications. Under such circumstances there is a demand to produce liquid display panels of different sizes. In particular, a variety of sizes are expected to be available in small liquid crystal display panels. The liquid crystal display panel uses an orientation film of polyimide or other suitable resin in order to orient liquid crystal. The orientation film has been formed by flexographic printing in the past.
However, the flexographic printing requires different plates for each type of orientation films to be printed. The production of the plate is a factor of the increase in the production cost of the liquid crystal display panel. In recent years, as a measure to solve this problem, there has been developed a process for applying the orientation film by inkjet printing. However, when the orientation film is formed by inkjet printing, it is necessary to reduce the viscosity of the orientation film when it is applied.
In this case, it is difficult to keep the orientation film in a predetermined area due to the reduced viscosity of the orientation film. For example, the orientation film flows to a portion of a sealing material for bonding the TFT substrate and the counter substrate together. When the orientation film is formed extending to the portion of the sealing material, the reliability of the sealing portion is reduced.
In order to prevent this, JP-A No. 145461/2008 describes a configuration in which ITO (Indium Tin Oxide), which is used as a pixel electrode, is formed to surround the display area so that the orientation film is confined to a predetermined range. In this way, the orientation film is prevented from extending to the sealing portion.
According to JP-A No. 145461/2008, the configuration for confining an orientation film to a predetermined range is as follows. In a frame area between the display area and the sealing portion, a concavo-convex pattern is formed in an insulating film and is coated with ITO constituting a pixel electrode. The concavo-convex pattern formed in the periphery of the display area prevents the orientation film with a low viscosity applied by inkjet printing, from extending beyond the periphery of the display area.
However, the thickness of the ITO formed in the periphery of the display area is equal to the thickness of the ITO of the pixel electrode, about 70 to 100 nm. It is not sufficient as a stopper for the orientation film whose thickness is about 150 nm. Further, the concavo-convex pattern is formed from an insulator with a thickness of about 300 nm, which is not sufficient to block the low viscosity orientation film.